1. Field of the Invention
The present invention relates to a zoom lens and, more particularly, to a solid-state two-group type retrofocus zoom lens that can be used in small image capturing devices such as camcorders and digital still cameras.
2. Description of Related Art
In recent years, the trend in image capturing devices has been for miniaturization. Because zoom lenses are key components of the image capturing devices, the trend has also been for small size, lightweight, and cheap lenses.
In the prior art, the design of the two-group type zoom lens used in a camera can generally be classified into two categories. The first is the telephoto type, which is a two-group type lens having a front group with a positive diopter and a rear group with a negative diopter. The air gap between the two groups is used to change the focal length. The telephoto type zoom lens is characterized by a shorter rear focal length by moving forwards the rear principal plane of the lens.
The second is the retrofocus type, which is a two-group type lens having a front group with a negative diopter and a rear group with a positive diopter. For example, U.S. Pat. No. 5,179,473 disclosed a retrofocus zoom lens with a zoom ratio that cannot exceed 2 but only reaches 1.8, thus being not able to meet the requirement of the high zoom ratio of recent image capturing devices. Retrofocus zoom lenses are also disclosed in U.S. Pat. No. 5,155,629 and U.S. Pat. No. 4,750,820, respectively. Because the size of a zoom lens strongly depends on the image sensor size, the ratio of the total track of the zoom system to the image sensor size is a key miniaturization parameter for the size of a zoom lens. This ratio should be made as small as possible. However, this ratio is about 10 in U.S. Pat. No. 5,155,629, and it is even larger than 16 in U.S. Pat. No. 4,750,820. In U.S. Pat. No. 5,1759,473, this ratio also reaches 14.